Perhaps I am confused and do not understand something in your question. The config-register has nothing to do with VTP. The config-register is something that the router (or perhaps a switch) reads at boot time to control its behavior. It has nothing to do with VTP. Is your question perhaps about changing the VTP version number?

HTH

Rick

Hello Sarah,

>> config-register number? my hunch is  it should increment the config-register so other switches  will not ignore the  vtp advertisment.

clearly you are thinking of VTP revision number as noted by Rick.

I'm not sure if the VTP revision number increments when setting a VTP version, but it cannot  cause it to be reset.

VTP clients if capable should follow the VTP version reported in server's VTP advertisement, as you guess increasing the revision number could be a way  to signal that something is changed but VTP message has also a VTP version field so a change in VTP version can be detected also in this way.

I haven't done tests specifically for this aspect so I may be wrong but the server could simply update the VTP version field in the VTP message.

Hope to help

Giuseppe

Yes, it increases the VTP revision ..

Rack1SW1#sh vtp st
VTP Version                     : running VTP1 (VTP2 capable)
Configuration Revision          : 6
Maximum VLANs supported locally : 1005
Number of existing VLANs        : 9
VTP Operating Mode              : Server
VTP Domain Name                 :
VTP Pruning Mode                : Disabled
VTP V2 Mode                     : Disabled
VTP Traps Generation            : Disabled
MD5 digest                      : 0x3F 0x9F 0x9D 0x60 0x97 0xEA 0x20 0x84
Configuration last modified by 0.0.0.0 at 3-1-93 01:05:26
Local updater ID is 0.0.0.0 (no valid interface found)

Rack1SW1#conf t

Rack1SW1(config)#vtp version 2

Rack1SW1(config)#end

Rack1SW1#sh vtp st
*Mar 16 16:35:58.205: %SYS-5-CONFIG_I: Configured from console by console
VTP Version                     : running VTP2
Configuration Revision          : 7
Maximum VLANs supported locally : 1005
Number of existing VLANs        : 9
VTP Operating Mode              : Server
VTP Domain Name                 :
VTP Pruning Mode                : Disabled
VTP V2 Mode                     : Enabled
VTP Traps Generation            : Disabled
MD5 digest                      : 0x65 0x27 0x6E 0x4F 0xD7 0x1D 0x73 0x9C
Configuration last modified by 0.0.0.0 at 3-16-93 16:35:56
Local updater ID is 0.0.0.0 (no valid interface found)
Rack1SW1#